We started using Khan Academy a few years back but truly only off and on. While the concept was good it was only somewhat user friendly when we first started.
With time they have made some changes and now we are hooked. My kids can follow along in order if they choose or move around to what interests them and as a homeschooling family this fits us perfectly. The true test for me and their worth came during the holiday season I ended up working full-time and was truly overwhelmed juggling it all and Khan Academy made the math very easy. My daughter was able to work by herself on the long days and I could easily follow up and see what progress she made give her any help she needed along the way. His videos made the confusion disappear. If I didn't answer her questions in the morning before I left or she found herself with new questions while I was away his videos would help. You work along and if you find you have questions the video attached to that lesson is on the same page you are working on, very convenient and easy to follow.
While math still frustrates my daughter (it has never been her favorite subject), she is getting a better understanding for it because he gives thorough information.
Oh and Khan Academy offers way more than math, that is just the only subject we are in need of at the moment. After watching the video introducing Computer Science I am hooked, I can't for my kids to get a look at that and for them to dig in. Hands on fun what can be better.
I hope you will get a chance to pop over to www.KhanAcademy.org and find something useful.